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Powell Point at the Top of the Grand Staircase

I’m in final preparation for a rafting exploration down the Green and Colorado Rivers in Canyonlands National Park with geologist Wayne Ranney, his geological entourage, and Colorado River and Trails Expeditions. In substitute for one of my regular posts, I offer a few views taken "here and there" on the Colorado Plateau.

Traveling north on the Cottonwood Canyon Road through the Kodachrome Basin, this spectacular scene is barely three miles from Cannonville, Utah on Scenic Byway 12. The vista is brought to you "in living color" courtesy of the San Rafael Group. The stratal package formed when a finger-like incursion of the newly-formed Pacific Ocean extended into the shallow Utah-Idaho trough during the Middle Jurassic. Also referred to as the Sundance Sea, its alternating sequences of red and brown marine mudstone and shale are interjected with light-colored beds of evaporite and eolian sandstone.

That’s Powell Point anoiting the summit of the Grand Staircase's Pink Cliffs in the background at 10,188 feet, the highest point of a geologic layercake that begins above the North Rim of the Grand Canyon in Arizona. This photo was taken from the broad bench below called the Skutumpah Terrace, built on softer, more erodible deposits such as the Carmel and the Entrada Formations of the aforementioned seaway.

The Point was named in 1879 by the geologist and explorer Clarence Dutton in honor of his famous contemporary John Wesley Powell, who first described the landscape of the region. Powell Point is held up by the white and pink limey cliffs of the Claron Formation, deposited during the Paleocene and Eocene around 55 million years ago in a vast system of shallow lakes and streams.

At one time, like the other High Plateaus of the region, Table Cliffs Plateau was capped by resistant basalt which served to protect the underlying Claron Formation from erosion. The Claron, being weakly lithified, assaulted by frequent freeze-thaw cycles at this lofty elevation, and winnowed away by headward erosion by the Paria River system, causes Powell Point to retreat as its cliffs are inexorably excavated away. On a grander scale, the Table Cliffs Plateau is situated on the east, high-side of the Paunsaugant Fault, a Basin and Range extensional fault that threatens the demise of the Colorado Plateau. It’s only a matter of time.

Stratigraphy.net | Impressum

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